The costs and benefits of symbiotic interactions: variable effects of rhizobia and arbuscular mycorrhizae on Vigna radiata accessions

Background The symbiosis among plants, rhizobia, and arbuscular mycorrhizal fungi (AMF) is one of the most well-known symbiotic relationships in nature. However, it is still unclear how bilateral/tripartite symbiosis works under resource-limited conditions and the diverse genetic backgrounds of the host. Results Using a full factorial design, we manipulated mungbean accessions/subspecies, rhizobia, and AMF to test their effects on each other. Rhizobia functions as a typical facilitator by increasing plant nitrogen content, plant weight, chlorophyll content, and AMF colonization. In contrast, AMF resulted in a tradeoff in plants (reducing biomass for phosphorus acquisition) and behaved as a competitor in reducing rhizobia fitness (nodule weight). Plant genotype did not have a significant effect on AMF fitness, but different mungbean accessions had distinct rhizobia affinities. In contrast to previous studies, the positive relationship between plant and rhizobia fitness was attenuated in the presence of AMF, with wild mungbean being more responsive to the beneficial effect of rhizobia and attenuation by AMF. Conclusions We showed that this complex tripartite relationship does not unconditionally benefit all parties. Moreover, rhizobia species and host genetic background affect the symbiotic relationship significantly. This study provides a new opportunity to re-evaluate the relationships between legume plants and their symbiotic partners. Supplementary Information The online version contains supplementary material available at 10.1186/s12870-024-05488-5.

observe each sight of root fragments under microscope and record the existance of the AMF structure a. individual: each plant has one phenotypic value; pool: individuals of the same accession under the same treatment in the same batch have a phenotypic value.FW: fresh weight.DW: DW, RCC: relative chlorophyll content.
Table S3.The analysis of variance (ANOVA) of all traits after log10 transformation.

Fig. S2
Fig. S2 Comparison of other plant traits under four treatments.(A) Plant fresh weight under four different treatments (control, Ri, Bj, Ri + Bj).(B) Plant dry weight, (C) leaf area-related traits, (D) RCC at different week-post-inoculation (wpi) under four treatments, (E) Root/shoot fresh weight (FW) ratio, (F) biomass-related traits, and (G) N and P content (mg/g) under different treatments.Bars represent the least squares mean, and error bars represent standard error (±SE).Different letters on the bars indicate significant differences (P < 0.05) under Tukey's HSD test.

Fig. S3
Fig. S3 Effect of mungbean subspecies and AMF treatment on the relationship between nodule weight and plant traits.Light red dash line: sublobata under Bj-only treatment; red line: sublobata under Bj+Ri treatment; light blue dash line: radiata under Bj-only treatment; blue line: radiata under Bj+Ri treatment.The lighter color range around every line represents 95% CI.

Fig. S4
Fig. S4 Comparison of RH-related and AMF-related traits in mungbean with Bj, Ri and Bj + Ri treatments.(A-G) Comparison of nodule-related traits with/without Ri under the presence of Bj. (H, I) Comparison of AMF-related traits with/without RH under the presence of Ri.Bars represent the least squares mean of the data after log transformation, and error bars represent ±SE.The asterisks represent statistical significance in analysis of variance (*: P < 0.05; **: P < 0.01; ***: P < 0.001).

Fig. S5
Fig. S5 Comparison of nodule-related traits in mungbean subspecies and accessions with Bj and Bj + Ri treatments.(A, C, E) Comparisons of nodule-related traits between two subspecies.(B, D, F) Comparisons of nodule-related traits among accessions.Bars represent the least squares mean of the data after log10 transformation, and error bars represent ±SE.Different letters on the bars indicate significant differences (P < 0.05) under Tukey's HSD test.

Fig. S6
Fig. S6 Comparison of red-nodule-related traits in mungbean subspecies and accessions with Bj and Bj + Ri treatments.(A) Comparisons of nodule FW among different accessions.(B, D, F, H) Comparisons of red-nodule-related traits between two subspecies.(C, E, G, I) Comparisons of red nodule-related traits among different accessions.Bars represent the least squares mean of the data after log10 transformation, and error bars represent ±SE.Different letters on the bars indicate significant differences (P < 0.05) under Tukey's HSD test.

Fig. S7
Fig. S7 Comparison of AMF-related traits in mungbean with Ri and Bj + Ri treatments.(A, C, E) Comparisons of AMF-related traits among different accessions.(B, D) Comparisons of AMF-related traits between two subspecies.Bars represent the least squares mean of the data after log10 transformation, and error bars represent ±SE.Different letters on the bars indicate significant differences (P < 0.05) under Tukey's HSD test.

Table S2 . The methods of trait measurement in this study. Trait Type a
put 3 leaves of the same branch per plant into L-type plastic folder and scan without petiole.The leaf area was measured by image J biggest leaf area individual mm 2 choose one biggest leaf per plant from the photo and measure the leaf area by image J

Analysis on V. radiata spp. radiata only
Data with Bj treatment and Bj+Ri treatment were used.S: two mung bean subspecies in the experiment, fixed effect.AMF: with or without Ri inoculation, fixed effect.Accession is a random effect nested within subspecies.Model = S + AMF + total nodule weight + S*AMF + S* total nodule weight + AMF* total nodule weight + S*AMF* total nodule weight + batch (random) + accession (nested within subspecies, random).* represents P < 0.05.** represents P < 0.01.*** represents P < 0.001.

Table S9 . The analysis of variance (ANOVA) of 20 mungbean accessions inoculated with two rhizobia after log10 transformation.
groups of cultivars and one wild mungbean group in the experiment, fixed effect.treatment: inoculated with Bj or Sf.Accession is a random effect nested within subspecies.Model = group + treatment + group*treatment + accession (nested within subspecies, random).* represents P < 0.05.** represents P < 0.01.*** represents P < 0.001.